When William Marshal was composing his will in 1219, he originally intended to allot nothing to his youngest son, Anselm, who was named after William's younger brother. It has been suspected that he wished for the young Anselm to rise from low rank to high on his own merits as William himself had done as a young knight errant. His advisors, however, convinced the ailing Marshal to grant Anselm a small piece of land.

The remarkable extinction of the male line of the Marshall family was credited to a curse bestowed upon the family in 1218 by Bishop of Ferns, Ailbe Ua Maíl Mhuaidh (died 1223). Each of the five sons of William Marshal, 1st Earl of Pembroke successively inherited the title, but, as Ua Maíl Mhuaidh predicted, none had children and the male line of the family died out.